The present invention relates to an arrangement for transforming a rotary movement of a smooth shaft into a thrust movement of a nut, and more specifically to a rolling nut for effecting this transformation.
Rolling nuts of the type under consideration have been known in the art.
One of such rolling or roller nuts is disclosed in applicant's U.S. Pat. No. 4,253,342. The disclosed arrangement includes three or four roller rings which have inner surfaces that roll on a smooth round outer surface of the shaft. The roller rings are mounted on the shaft so that they are inclined to the axis of the shaft and are with that shaft in a friction contact connection. The contact surfaces of the shaft and the roller rings are so selected that the rolling tracks of the roller rings describe on the shaft uniform helical lines. The roller rings are accommodated in a two-part housing which is provided with corresponding recesses for receiving the roller rings and with elastic means which generate pressure forces (friction contact) between the roller rings and the shaft. Such rolling nuts have a high accuracy, however in many cases they are too expensive and too special. For example, it is difficult or impossible with this construction to readjust the direction of the pitch from the left hand to the right hand or to one or another value of the pitch. The disadvantage of these otherwise satisfactory roller nuts resides in the subdivision of the housing into two parts, which always requires a multiple readjustment and bolting of those two parts to each other.
It is a great advantage of the known roller nuts that they are accommodated in a closed housing. However, such a protection by the enclosed housing is not always necessary in practice. Very often small dimensions of the entire constructions appear to be more important than the protection of the roller rings. This can be achieved by a so-called open rolling nut arrangement, in which no housing, which encloses the roller rings, is employed. The risk of contamination is very insignificant when the roller rings with sealing discs are employed, as is in the case of roller bearings.